1. Field of the Invention
This invention relates to a novel rubber crawler, and more particularly to a rubber crawler having a structure for preventing the occurrence of crack or breakage in each of the widthwise edge portions of rubber in the crawler.
2. Description of Related Art
There are well-known and widely used two types of rubber crawlers having structures shown in FIG. 1 and FIG. 2. The first type rubber crawler shown in FIG. 1 comprises an endless rubber belt 1, a plurality of core metal pieces 2 arranged and buried at predetermined intervals in the longitudinal direction of the belt 1, and steel cords 3 arranged to cover the outer surface of the metal pieces 2 and buried in the longitudinal direction of the belt 1. Since a widthwise length of the metal piece 2 is shorter than a full width of the belt 1, widthwise edge portions 4 made from only rubber are formed in both sides of the belt 1. On the other hand, the second type rubber crawler shown in FIG. 2 comprises rubber pads 5 fixed to links 6, which being axially supported by pins 7 form an endless structure, through metal crawler blocks 8 and bolts and nuts 9. In the latter case, a widthwise length of the rubber block 8 is shorter than a full width of the rubber pad 5, so that widthwise edge portions made from only rubber are formed in both sides of the rubber pad 5.
In general, the widthwise edge portion of the core metal piece has a vertically cut shape at its widthwise edge and front and back edges and is the most flexible portion of the rubber crawler, so that deformation strain is liable to be most caused in the widthwise edge portion at a use state of the rubber crawler. For example, when the rubber crawler contacts with or rides on protrusions such as pebbles, stone pieces, and the like scattered on a running road or a curb of a footpath as shown in FIG. 3, the widthwise edge portion 4 is sandwiched between the core metal piece 2 (or metal crawler block) and the curb 10 and shearing force strongly and repeatedly acts to the widthwise edge of the core metal piece during the running of the rubber crawler to thereby create crack C from the vicinity of such an edge toward an outer surface of the widthwise edge portion 4. See FIG. 3 a crack grows toward the side of contacting with ground and further toward the front and back sides of the widthwise edge portion due to repetition of deformation stress to finally cause breakage of the widthwise edge portion. As a result, the durability of rubber constituting the widthwise edge portion and hence service life of the rubber crawler are undesirably degraded.